This invention relates to an arrangement for service, maintenance and installation at subsea locations by means of which an operator or diver can be located within a bell and from the interior of the bell operate devices for working at depths within the sea, for example, on wells in offshore petroleum recovery arrangements.
More and more in recent years there has been an increase in offshore gas and petroleum well drilling and recovery and interest increases more and more both in terms of the area where such drilling can occur and the water depths at which these can occur.
Methods had orginally been used at shallower depths where divers of various types within the water could provide the maintenance and manipulation and connecting steps necessary during preparation of a well. However, this provides severe limits on the time within which a diver may operate and causes considerable mental and physiological strain on the diver.
Therefore, automatic or remote or robot devices have been used in order to avoid the need for divers, they being controlled from the surface. However, it is important that man be located at the place where maintenance and construction or fabrication is being performed so as to deal with any trouble areas that occur and also to better analyze the situation.
This has led in most recent years to the use of manned bells, preferably atmospheric type, so that decompression is not a problem that needs to be contended with, since it creates problems even when saturation diving is used and also creates enormous expenses.
Apparatus is disclosed in U.S. Pat. No. 3,302,709 for working at an underwater well base. This arrangement provides for automatic devices which use guide lines from a surface location to the subsea well for directing the devices.
A salvaging method is disclosed in U.S. Pat. No. 1,469,574 which includes the use of parallel spaced apart guide rods extending from a salvaging ship to a sunken vessel and along which a frame is guided from the surface to the sunken vessel. The frame has the salvaging mechanism such as locating, cutting, and grappling mechanisms mounted thereon.
A diver controlled salvage bell is disclosed in U.S. Pat. No. 2,320,696, from which the operator within the bell may control movement of the bell with respect to a sunken ship and the diver may, for example, move the device laterally or vertically to position it while it is under water.
U.S. Pat. No. 3,851,491 discloses an underwater bell chamber provided with arms and grippers. The bell is guided along the guide wires from the surface to the subsea well by moving along the guide wires. The grippers are controlled by an operator within the chamber in order to stop and lock movement of the chamber by gripping the guide wires.